Thread: Eight Queen Problem code. But I cannot understand.

Eight Queen Problem code. But I cannot understand.
Can anybody explain it for me briefly?
Thank you so much!

Code:

#include <stdio.h> 
#include <stdlib.h> 
#define N 8 

// int num; 

void backtrack(int* column, int* rup, int* lup, int* queen, int); 

int main(void) { 
    //num = 0;
    int column[N+1]; 
    int rup[2*N+1]; 
    int lup[2*N+1]; 
    int queen[N+1] = {0}; 

    int i; 
    for(i = 1; i <= N; i++) 
        column[i] = 1; 
    for(i = 1; i <= 2*N; i++) 
        rup[i] = lup[i] = 1; 

    backtrack(column, rup, lup, queen, 1); 

    return 0; 
} 

void printQueen(int* queen) {
    int x, y;
    // printf("\nAnswer %d\n", ++num);
    for(y = 1; y <= N; y++) {
        for(x = 1; x <= N; x++) {
            printf(" %c", queen[y] == x ? 'Q' : '.');
        }
        printf("\n");
    }
    printf("\n");
}

void backtrack(int* column, int* rup, int* lup, int* queen, int i) { 
    if(i > N) { 
        printQueen(queen);
    } 
    else { 
        int j;
        for(j = 1; j <= N; j++) { 
            if(column[j] == 1 && 
                 rup[i+j] == 1 && lup[i-j+N] == 1) { 
                queen[i] = j; 
                // mark
                column[j] = rup[i+j] = lup[i-j+N] = 0; 
                backtrack(column, rup, lup, queen, i+1); 
                column[j] = rup[i+j] = lup[i-j+N] = 1; 
            } 
        } 
    } 
}

The main problem for me is I can not understand the two array rup[] and lup[].

Code:

#include <stdio.h> 
#include <stdlib.h> 
#define N 8 

// int num; 

void backtrack(int* column, int* rup, int* lup, int* queen, int); 

int main(void) { 
    //num = 0;
    //creates arrays
    int column[N+1]; 
    int rup[2*N+1]; 
    int lup[2*N+1]; 
    int queen[N+1] = {0}; 

    int i; 
    // Fills columns with 1
    for(i = 1; i <= N; i++) 
        column[i] = 1; 
   // this is really strange, I don't know if it's possible, it equals rup[i] to lup[i] and lup[i] to 1 if I'm not wrong
    for(i = 1; i <= 2*N; i++) 
        rup[i] = lup[i] = 1; 

    backtrack(column, rup, lup, queen, 1); 

    return 0; 
} 

void printQueen(int* queen) {
    int x, y;
    // printf("\nAnswer %d\n", ++num);
    for(y = 1; y <= N; y++) {
        for(x = 1; x <= N; x++) {
            printf(" %c", queen[y] == x ? 'Q' : '.'); // I think that if queen[y] equals to x "Q" is printed, else "." is printed
        }
        printf("\n");
    }
    printf("\n");
}

void backtrack(int* column, int* rup, int* lup, int* queen, int i) { 
    if(i > N) { 
        printQueen(queen);
    } 
    else { 
        int j;
        for(j = 1; j <= N; j++) { 
            if(column[j] == 1 && 
                 rup[i+j] == 1 && lup[i-j+N] == 1) { 
                queen[i] = j; 
                // mark
                column[j] = rup[i+j] = lup[i-j+N] = 0; 
                backtrack(column, rup, lup, queen, i+1); 
                column[j] = rup[i+j] = lup[i-j+N] = 1; 
            } 
        } 
    } 
}

It's interacting with the int arrays and printing..